1. Field of the Invention
The present invention relates to an organic electroluminescence (hereinafter, simply referred to as “EL”) light-emitting device utilizing EL of an organic compound material which emits light when current is injected therein, and a production method thereof. More particularly, the present invention relates to an organic EL light-emitting device having banks for isolating pixels, and a production method thereof.
2. Description of the Related Art
In the production of the organic EL light-emitting device, which is promising for a large-area display, an organic EL light-emitting material has been applied to a large-size substrate in an attempt to reduce the production cost.
Japanese Patent Application Laid-Open No. H10-153967 discloses a method of fabricating a light-emitting device using an inkjet system, which is a typical method for applying such a material. The method is described below.
As shown in FIG. 8, transparent anode electrodes 82 made of indium tin oxide (hereinafter referred to as “ITO”) or the like are fabricated on a transparent substrate 81 using photolithography. Then, “banks” 83 (of polyimide, for example) for pixel isolation having high electrical insulation properties are formed between the transparent electrodes 82 using photolithography. Then, layers, such as a hole injection layer and a light-emitting layer, are formed in the mentioned order in each of the pixels, by dropping and coating with the aid of an inkjet system. At this time, the height of each of the “banks” needs to be sufficiently large with respect to the thickness of the organic EL layer. The purpose of this is to prevent such a phenomenon that when an organic EL material is ejected from a nozzle 85 of an inkjet system (not shown) and arrives at each of the pixels, a part of the material bounces from the substrate to be scattered to the periphery of the pixel and be mixed into an adjacent organic EL material across the bank. In the figure, reference characters 84a, 84b, and 84c denote organic EL materials for red, blue, and green, respectively. Further, as shown in FIGS. 9A and 9B, banks 91 of a column direction and banks 92 of a row direction are formed into shapes for surrounding each of the pixels for accomplishment of isolation between the pixels. In the figures, reference characters 93a, 93b, and 93c denote organic EL materials for red, blue, and green, respectively. Thus, as disclosed in Japanese Patent Application Laid-Open No. H10-153967, in the case of the inkjet system, the heights of the “banks” are substantially identical at any location (i.e., h5=h6 in FIG. 9B).
Next, Japanese Patent Application Laid-Open No. 2002-075640 discloses a method of fabricating a light-emitting device using the so-called nozzle printing, which is another method for applying an organic EL material. The method is described below.
As shown in FIG. 6, after forming transparent anode electrodes 62 made of ITO on a transparent substrate 61 by using photolithography, “banks” 63 suitable for nozzle printing and for pixel isolation formed in a striped pattern (corresponding to banks 73 of a column direction in FIG. 7) by photolithography. In this case, the heights of the banks need to be sufficiently large to such an extent that required amounts of applied inks (organic EL materials 64a, 64b, and 64c for red, blue, and green, respectively) do not get over the banks 63 and to also be substantially identical at any location (see FIG. 6). A nozzle 65 is moved at a high speed along the striped banks 73. The characteristic of the nozzle printing is that the viscosity and pressure of a solution (for example, organic EL material 64 for red) are adjusted, so that a required amount of the solution can be dropped into a groove portion between banks with one ejection. That is, by continuously dropping the organic EL material in the groove (without any break, as in the case of drawing a continuous line with a single stroke of an ink pen), the problem of “contamination of ink (color mixing) due to bouncing back of liquid droplet across bank” in the ink jet system is overcome. The technique of dropping an organic EL material in a groove in a continuous manner (without any break, as in the case of drawing a continuous line with a single stroke of an ink pen) is hereinafter referred to as “nozzle printing”.
However, as disclosed in Japanese Patent Application Laid-Open No. 2002-075640, in the case of the nozzle printing, because the “banks” 73 are provided in the striped pattern (see FIG. 7), there is no physical isolation between pixels of the same color disposed in a direction 76 in which the relative positional relationship between a nozzle 75 and a formed film-shaped member changes (hereinafter referred to as “scanning direction”). Accordingly, there is posed the problem of crosstalk between adjacent pixels of the same color. The crosstalk is attributable to the transmission of light emitted by a light-emitting layer between adjacent pixels of the same color through organic compound layers, such as the light-emitting layer, a hole-transporting layer, and an electron-transporting layer.